This invention relates to cryostats used in magnetic resonance (MR) imaging and more specifically to ferromagnetic shields for the magnets located in the magnetic resonance cryostats.
Magnetic resonance magnets used in medical diagnostics generate high intensity dc magnetic fields. Installations of MR equipment, where practicable, are located in a separate building in an open area. In hospitals in crowded metropolitan areas where space is at a premium, it is desirable to have as little disturbance to other hospital facilities as possible. Without special shielding a large area surrounding the magnet is needed to assure a minimum of interference with other diagnostic equipment and patients with cardiac pacemakers or neurostimulators.
To reduce space requirements for MR magnet installations, shielded rooms have been erected surrounding the machines. The shielding has to be designed for the particular room shape and the shielding typically creates structural loading problems.
Another approach to reduce space requirements for MR magnets is to use a shield comprising multiple steel components assembled around the cryostat of MR magnet. For example, in U.S. Pat. No. 4,646,045 entitled, "Aperture Sized Disc Shaped End Caps of a Ferromagnetic Shield For Magnetic Resonance Magnets" assigned to the same assignee as the present invention a shield is added around the magnet with the shield designed to minimize the perturbation of the field in the working area of the magnet. The cost of this type of shield can typically be $100K or more. As a result a shielded MR magnet is typically more expensive than an unshielded one.
It is an object of the present invention to provide a shielded MR magnet at reduced cost.